Move py.typed file into main package

[ArBridgeman]

Currently, the py.typed file is located at exasol/saas/client/openapi/py.typed. In order for it to be correctly parsed for the pytest-* libraries, we need it located higher, I think in exasol/saas, but this should be verified, as it could be ok at exasol/saas/client.

The error observed is:

exasol/pytest_saas/__init__.py:6:1: error: Skipping analyzing "exasol.saas": module is installed, but missing library stubs or py.typed marker  [import-untyped]
    from exasol.saas import client as saas_client
    ^
exasol/pytest_saas/__init__.py:7:1: error: Skipping analyzing "exasol.saas.client.api_access": module is installed, but missing library stubs or py.typed marker  [import-untyped]
    from exasol.saas.client.api_access import (
    ^